A known example of an ultrasonic atomizer of this type is described in the specification of Japanese Utility Model Application Laid-Open No. 3-15674. The atomizer described in this literature is characterized by use of a mesh plate having tapered minute holes which flare from one side of the plate toward the other. The mesh plate is arranged in such a manner that the side in which the minute holes have the openings of larger diameter opposes the upper end face of the pump shaft of an ultrasonic pump, and such that a minute gap is produced between the mesh plate and the upper end face of the pump shaft.
In an ultrasonic atomizer, it is important to achieve balance between the amount of liquid pumped by the ultrasonic pump and the amount of atomization produced by the mesh plate. When there is a minute gap between the upper end face of the pump shaft and the mesh plate, as in the document mentioned above, the amount of liquid pumped tends to be larger than the amount of liquid atomized. The liquid that is not atomized flows down from the gap to the upper portion (the horn) of the pump shaft and becomes a load on ultrasonic vibration at the horn. This causes an unstable spraying operation and can lead to cessation of operation in some cases.
Another problem is that the user's fingers become soiled when liquid that has not been atomized flows out of the device. An important technical problem is assuring the liquid tightness of the device.
The number of minute holes formed in the mesh plate has a direct influence upon the amount of atomization. The greater the number of minute holes per unit surface area, the greater the amount of atomization. When the number of minute holes is increased, however, there is a decline in the strength of the mesh plate itself. There is a need for some expedient which can provide strength while allowing an increase in the number of minute holes.
Since the mesh plate described in the above-mentioned document is such that the minute holes have aperture diameters that differ on the two sides of the plate, care must be taken in terms of the orientation of these sides when the mesh plate is mounted in the atomizer.
An ultrasonic atomizer can be applied to an ultrasonic inhaler, as set forth above. Medicines of higher cost than inexpensive water and physiologic saline solutions are often used in inhalers. Accordingly, arranging it so that every drop of the medicine is used once the inhaler has been filled is important in terms of economy.
Another requirement of an inhaler is that the user repeat the operation for spraying the inhalant and halt this operation in conformity with breathing. Control of the spraying operation is achieved by having the user turn an operating switch on and off. However, turning the operating switch on and off often is troublesome or difficult particularly for the elderly or children. There is a need to arrange it so that the liquid is sprayed automatically and intermittently in conformity with the user's breathing.